A bill of exchange is a future payment instrument. If drawn "payable one month after date" on 1st July 2021, its initial due date is 1st August 2021. The Negotiable Instruments Act adds three days of grace. Thus, the final maturity date is 1st August 2021 + 3 days = 4th August 2021. Therefore, the maturity date is 4th August 2021, making option (A) 4th August 2021 the correct answer.